This course is addressed to students and researchers interested
in logics for reasoning about multi-agent belief revision,
belief updates and knowledge updates induced by various forms of
communication or interaction. It is a foundational course,
designed to present to students and researchers from other
fields the work done in recent years by a number of researchers
on integrating ideas from Belief Revision Theory within the DEL
(Dynamic-Epistemic Logic) paradigm. The course is
self-contained, not assuming any background knowledge, but
presupposing only some general experience or facility with using
logical languages, the concepts of syntax and semantics etc. We
start by presenting the main notions of "standard
DEL", arguing that this logic is appropriate for updating
"hard information" (unrevisable knowledge), but that
it is inappropriate for "soft information" (possibly
false beliefs or defeasible knowledge). We then present
"belief-revision models", defining some important
epistemic/doxastic notions, considering a number of logical
languages for these models, and explaining the relevance of
these notions to fundamental issues in contemporary
Epistemology, in Computer Science and in the study of language
and communication. We present various Belief Update operations
and various belief-revision policies proposed by different
authors, focusing on one particular proposal (the
Action-Priority Update) of great generality and elegance. We
present reduction laws (the "dynamic laws of Interactive
Belief Revision"), complete axiomatizations, applications
to dialogue games and communication strategies, connections with
other research areas and open problems.